1. Field of the Invention
Aspects of the present invention relate to an optical disc apparatus and a method of driving the same, and more particularly, to a near-field optical disc apparatus and a method of driving the same to prevent a light focusing element and a disc from colliding with each other due to overshoot generated in a gap pull-in method, and to provide fast loading of the disc as an actuator approaches a near-field.
2. Description of the Related Art
Recently, a near-field optical disc apparatus that achieves a large storage capacity and a high Data Transfer Rate (DTR) has been proposed. The near-field optical disc apparatus is also known as a near-field recording system. The near-field optical disc apparatus records and/or reproduces data in a disc by using light in a near-field in which the light is not diffracted. Thus, the near-field optical disc apparatus has to control a gap distance between the end surface of a Solid Immersion Lens (SIL) attached to a light focusing element, such as an object lens, and an optical disk such that the gap distance becomes very small (for example, several nanometers).
A near-field optical system based on the SIL has to follow a disturbance of a disc within a range of a near-field, and thus, cannot use a focusing servo method which is used in a conventional far-field optical disc drive. Hence, the near-field optical system uses a mode switching pull-in method. The mode switching pull-in method has three stages, which are an approach stage, a handover stage, and a gap servo stage. In the approach stage, a linear output voltage is applied to an actuator by an open loop to move the actuator toward a near-field area in which a sensing operation can be performed. The actuator approaches a disc as the actuator moves toward and through the near-field area. In the handover stage, a speed of the actuator is controlled by a regular input to move the actuator toward and/or to a target location so as to prevent collision with the disc. In the gap servo stage, a disturbance of the disc is performed at the target location. The gap servo stage corresponds to a focusing servo stage in the conventional far-field optical disc drive.
However, the mode switching pull-in method may overshoot the target location, which causes collisions between the SIL and the disc, and requires determining/obtaining information on a location of the disc for loading the disc, which takes time.